Mechanization of Cognition - Biomimetics: Biologically Inspired Technologies - page 103

Figure 3.A.1 Thalamocortical modules. All cognitive information processing is carried out by distinct, modular,
thalamocortical circuits termed feature attractors; of which two are shown here. Each feature attractor module (of
which human cortex has many thousands) consists of a small localized patch of cortex (which may be comprised of
disjoint, physically separated, sub-patches), a small localized zone of thalamus, and the reciprocal axonal con-
nections linking the two. When referring to its function (rather than its implementation, a feature attractor is termed a
lexicon). Each feature attractor module implements a large stable set of attractive states called symbols, each
represented by a specific collection of neurons (all such collections within a module are of approximately the same
size). Neuron overlap between each pair of symbols is small, and each neuron involved in representing one symbol
typically participates in representing many symbols. One item of knowledge is a (parallel, two-stage synfire) set of
unidirectional axonal connections collectively forming a link between the neurons representing one symbol within
one feature attractor (e.g., the green one shown here) and neurons representing one symbol on a second feature
attractor (e.g., the blue one shown here). The collection of all such links between the symbols of one module
(here the green one), termed the source lexicon, and that of a second (here the blue one), termed the target lexicon,
are termed a knowledge base (here represented by a red arrow spanning the cortical portions of the green and blue
modules).
subsequently excite other neurons of Layers II, III, and IV. As mentioned above, no attempt to
discuss the details of this module design will be made, as these details are not yet adequately
established and, anyway, are irrelevant for this introductory sketch. Instead, a discussion is now
presented of a simple mathematical model of an attractor network to illustrate the hypothesized
dynamical behavior of a thalamocortical model in response to proper knowledge link and operation
command inputs.
The theory hypothesizes that each thalamocortical module carries out a single information
processing operation — confabulation. This occurs whenever appropriate knowledge link inputs
and the operation command input arrive at the module at the same time. The total time required for
the module to carry out one confabulation operation is roughly 100 msec. Ensembles of mutually
interacting confabulations (instances of consensus building — see the main Chapter) can often be
highly overlapped in time. By this means, the ''total processing time'' exhibited by such a consensus
building ensemble of confabulations can be astoundingly short — often a small multiple of the
involved axonal and synaptic delays involved; and not much longer than a small number of
individual confabulations. This accounts for the almost impossibly short ''reaction times'' often
seen in various psychological tests.